I always put such things in the positive promt: Adult, mature, full grown Ect, ect, ect.

It churns out a 5-10 year old 80% of the time.

Using either the furry - cinematic or furry - digital painting

Anthro art style, zoomorphism character, anthropomorphic in the style of furry art, anthropomorphic animal. Pulitzer Prize-winning photojournalism, adult white furred anthro skunk male, full body portrait, tall lean build, athletic build, mature male, pristine white fur without markings, fluffy tail visible in background, tousled white hair, cobalt blue eyes, soft fur texture, well groomed fur, smooth high definition fur, rueful expression, relaxed pose, soft lighting, celestial aesthetic, bedroom background, high detail, furry, solo character, Wearing sleeveless jacket of pockets and loose cargo pants torn off at the calf, no shoes

I get 20 'underage' results like this

For every 1 'mature' result like this